1. Field of the Invention
The present invention relates generally to the field of optical devices. More particularly, the invention relates to optical isolators and methods of preventing optical feedback. The invention also relates to methods of making optical isolator assemblies.
2. Description of the Related Art
Silica-based optical fiber is widely used for communication systems. To effectively utilize optical fiber systems, a variety of in-line optical components have been created to deal with physical limitations or to boost line efficiency. However, the placement of components into optical fiber lines, while solving some problems, also creates new problems. One such problem which plagues optical communication systems is the occurrence of diverse return beams, also known as reflections, originating from components spliced into the optical fiber.
Diverse return beams cause a variety of negative effects, including disruption of the oscillation of a laser or light source and disruption of amplifiers within the line. Optical isolators are used to reduce or eliminate the negative effects of diverse return beams. Isolators allow transmission of optical beams in a forward direction while eliminating any beam traveling in the reverse direction.
Prior art devices, characterized by half-wave plates, generally require precise alignment of components. The assembly of these devices has traditionally been performed on an individual basis (one at a time) because of the need for precise angular and translational alignment of each component. In addition, the prior art devices may be sensitive to wavelength, temperature and other conditions.
U.S. Pat. No. 5,774,264 (Konno) describes an isolator with three birefringent plates and two Faraday rotators. The isolator described in the Konno patent purportedly reduces polarization dispersion. U.S. Pat. No. 5,499,307 (Iwatsuka) shows an isolator design using two birefringent plates separated by a Faraday rotator and a half-wave plate. U.S. Pat. No. 5,446,813 (Lee) describes the use of a first lens to converge incoming beams into parallel beams in connection with an isolator assembly including first and second birefringent plates separated by a Faraday rotator.
U.S. Pat. No. 5,559,633 (Emkey) describes an optical isolator that has a non-reciprocal rotator disposed between birefringent wedges. The Emkey patent also describes the use of an above normal incident angle of an incoming light beam to reduce walk-off effects. U.S. Pat. No. 5,566,259 (Pan) shows the use of two successive stages of isolation, each incorporating birefringent wedges separated by a Faraday rotator.